The present invention is directed to a system and method for determining engine torque for use in controlling a powertrain.
Mechanical throttle control systems use airflow as the primary control parameter in controlling powertrain output. The airflow is controlled by a throttle valve in the intake which is mechanically linked to a throttle pedal. As such, many powertrain control parameters were traditionally based on, or indexed by, the throttle valve position.
Electronic airflow control systems, such as variable cam timing systems and electronic throttle control systems, replace the traditional mechanical throttle cable system with an xe2x80x9celectronic linkagexe2x80x9d provided by sensors and actuators in communication with an electronic controller. This increases the control authority of the electronic controller and allows the airflow to be controlled independently of the accelerator pedal position. As such, the throttle valve position is no longer necessarily indicative of the requested or desired powertrain output.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a system and method for determining engine torque for use in controlling a powertrain to achieve a desired powertrain output, such as engine torque, wheel torque, wheel power, or tractive effort.
Another object of the present invention is to provide a system and method for determining a desired engine torque during a ratio change of an automatic transmission.
In carrying out the above object and other objects, advantages, and features of the present invention, a system and method for controlling a vehicular powertrain preferably including an internal combustion engine and an automatic transmission include determining a desired wheel torque, determining engine speed, determining turbine speed, determining a selected gear and associated selected gear ratio, determining a transmission spin loss based on a first function of the turbine speed and the selected gear, determining a torque converter multiplication, determining a transmission torque proportional loss based on a second function of the turbine speed and the selected gear, determining a desired engine torque based on the transmission spin loss, the transmission torque proportional loss, the torque converter multiplication, and the selected gear ratio, and controlling the powertrain using the desired engine torque such that actual wheel torque approaches the desired wheel torque. A transmission pump loss may also be determined, based on line pressure and engine speed, and incorporated into the determination of desired engine torque.
An alternative strategy for determining desired engine torque uses a power-based calculation if the vehicle speed is above a predetermined threshold, and a gear, ratio based calculation if the vehicle speed does not exceed the predetermined threshold. Turbine speed (actual or estimated) or torque converter slip may be used in determining the desired engine torque according to the present invention.
Alternative strategies for determination of the desired or requested engine torque during a gear shift or ratio change are also provided. The first strategy determines engine torques corresponding to the current gear ratio and the target gear ratio. The desired engine torque is then interpolated between the torque values corresponding to the current gear ratio and the target gear ratio based on the turbine speed. Turbine speed is used to interpolate between the two values by comparing the actual or estimated turbine speed to the expected turbine speed for the current and target gears or gear ratios. Turbine speed may be determined by an appropriate sensor or estimated.
The second strategy utilizes a sample and hold technique to determine the desired engine torque during a ratio change. Upon initiation of a ratio change, the estimated value for the torque converter slip is held or stored for a predetermined time. This value is used to determine the desired engine torque based on one of the two alternative strategies described above.
The first strategy is preferred in that it is capable of integrating relatively complex expressions for the engine torque calculation, is not susceptible to delays in gear ratio determination, and the same calculation provides acceptable results over the entire vehicle speed range.
The present invention provides a number of other advantages over prior art control strategies. For example, the present invention provides a modular control structure which may be easily adapted to new engine technologies such as lean burn, variable cam timing, and direct injection. Electronic airflow control provides improved powertrain efficiencies and better control during various modes of operation including cruise control and traction assist.
The above advantages and other advantages, objects, and features of the present invention, will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.